Method for purging dip forming crucible environment

ABSTRACT

IN ACCRETING MOLTEN MATERIAL ONTO A CONTINUOUS, ELONGATED CORE, THE CORE IS PASSED UPWARDLY THROUGH A CRUCIBLE CONTAINING A MOLTEN BATH OF THE MATERIAL, AND EXITS THROUGH AN ELONGATED TUBE EXTENDING UPWARDLY FORM THE CRUCIBLE AND IS THEN COOLED. AN INERT GAS IS INTRODUCED TO THE CRUCIBLE ABOVE THE MOLTEN MATERIAL AT A PRESSURE SUFFICIENT TO MAINTAIN A CONTINUOUS FLOW OF GAS THROUGH THE TUBE OUTWARDLY FROM THE CRUCIBLE, AND COOLANT (E.G. WATER) PENETRATING THE TUBE OR CRUCIBLE IS ATOMIZED AND/OR VAPORIZED AND IS CONVEYED CONCURRENTLY WITH THE GAS STREAM.

N. J. LIPSTEIN 3,813,260

METHOD FOR PURGING DIP FORMING CRUCIBLE ENVIRONMENT May 28 1974 2 Sheets-Sheet l Original- Filed March 8,

[)7 vent or (Vorman cZL/pse/h, b H/is At or'ney May 28, 1974 J. LIPSTEIN 3 5 METHOD FOR PURGING DIP FORMING CRUCIBL E ENVIRONMENT Original Filed March 8, 1967 .2 Sheets-Sheet 2 IN VEN TOR. NORMAN J L IPSTE/N United States Patent Office 3,813,260 Patented May 28, 1974 3,813,260 METHOD FOR PURGING DIP FORMING CRUCIBLE ENVIRONMENT Norman Jay Lipstein, Schenectady, N.Y., assignor to General Electric Company Continuation of application Ser. No. 99,690, Dec. 18, 1970, which is a continuation of application Ser. No. 871,593, Nov. 3, 1969, which is a continuation of application Ser. No. 633,325, Mar. 8, 1967, which in turn is a continuation-in-part of application Ser. No. 538,370, Mar. 29, 1966, all now abandoned. This application Feb. 7, 1972, Ser. No. 224,329

Int. Cl. C23c 1/10, N12

US. Cl. 117-114 R 3 Claims ABSTRACT OF THE DISCLOSURE In accreting molten material onto a continuous, elongated core, the core is passed upwardly through a crucible containing a molten bath of the material, and exits through an elongated tube extending upwardly from the crucible and is then cooled. An inert gas is introduced to the crucible above the molten material at a pressure sufficient to maintain a continuous flow of gas through the tube outwardly from the crucible, and coolant (e.g. water) penetrating the tube or crucible is atomized and/or vaporized and is conveyed concurrently with the gas stream.

BACKGROUND OF THE INVENTION This application is a continuation of my copending application for patent Ser. No. 99,690, filed Dec. 18, 1970, and now abandoned, which application in turn was a continuation of my then copending but now abandoned application for patent Ser. No. 871,593, filed Nov. 3, 1969, which in turn was a continuation of my then copending but now abandoned application for patent Ser. No, 633,325, filed Mar. 8, 1967, which in turn was a continuation-inpart of my then copending but now abandoned application for patent Ser. No. 538,370, filed Mar. 29, 1966.

DESCRIPTION OF THE PRIOR ART The clip forming process, such as used in casting metal, is now well known in the art. According to this process, an elongated body such as a metal rod is typically pretreated by passing it through a straightener, a surface cleaning apparatus and desirably through a drying means, and then through a vacuum entrance chamber positioned below or at the bottom of a crucible containing a bath of molten material. A continuous, elongated core or body is passed upwardly through the molten bath, which bath may have the same chemical composition as that of the core or a different composition. The molten material in the crucible accretes or deposits upon the outer surface of the core thereby increasing its cross-sectional area appreciably. After emerging from the crucible, the resulting cast member is cooled as by a water spray from one or more jet nozzles at least sufficiently so that the cast member can be rolled or worked. From there, the cast member may be passed through a suitable roll mechanism where it is drawn and reduced in cross-sectional area and then passed to a suitable receiving means such as a take-up reel.

SUMMARY OF THE INVENTION In the dip forming process water in close proximity to hot molten bath is converted to steam, resulting in a corresponding increase in volume that can cause a rapid increase in pressure, equivalent -to an explosion. Further, water or steam may dissociate and the elemental hydrogen and oxygen can be dissolved by and/or react with the molten material. The oxygen may result in the formation of undesirable oxides. Also, the presence of hydrogen alone, or hydrogen and oxygen concurrently, in molten metal in sutficient amounts will cause formation of gas bubbles upon solidfication of the accreted material on the cast member. The formation of oxides, gas bubbles and/ or voids not only adversely affects the quality of the product, but also deleteriously affects the uniform accretion of molten material onto the core by creating regions of relatively poor thermal conductivity within a mass of relatively good thermal conductivity. Thus, the effect of oxygen and hydrogen is not confined to the oxide phases and bubbles they create, but is magnified due to the irregularities in heat transfer they produce, causing substantial nonuniformity in the external contour of the accreted coating. Bubbles, voids, oxide phases, internal discontinuities, and irregular accretion are all undesirable in that they promote or cause the formation of cracks and fissures when stresses are imposed, as by bending, rolling, drawing or the like. A product manifesting such defects is generally not acceptable.

Even after the molten material has accreted to the core and the cast member has emerged from the molten bath, it is desirable to prevent contact of the hot cast member with oxygen. For example, in dip forming copper, oxygen from the air or from dissociated water will react with the hot copper to produce copper oxide, which can harmfully affect the response of the rod in subsequent rolling or drawing operations.

OBJECTS OF THE INVENTION This invention has, therefore, as its object to provide for use in dip forming a method and apparatus to purge the environment of the molten bath material and hot cast member from deleterious gaseous contaminants.

This object together with other objects and advantages may best be understood by referring to the following detailed description, and to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a perspective view, partly in section, of an apparatus practicing my present invention;

FIG. 2 shows a cross section of the wire dip crucible of my invention; and

FIG. 3 is a velocity profile of the purge stream for the system.

DESCRIPTION OF A PREFERRED EMBODIMENT In the drawings, there is shown a preferred embodiment for practicing the invention, and although the invention is described hereinbelow with particular reference to forming copper rod, it should be understood that the invention is applicable for producing other stock such as sheet, tube or strip and of materials or metals. Referring to FIG. 1, a continuous core rod of copper 1 is introduced to a drawing apparatus and shaving equipment 2 where the oxide coating or other surface contaminants are removed therefrom. If desired, other means may be utilized for cleaning the suface of the rod. The rod is passed through drive means 3 and enters through nozzle 4 located in the bottom of crucible 8 which contains a molten bath of copper '5. The molten copper is supplied to the crucible from a suitable source such as an electric induction heated furnace (not shown), and the crucible is maintained at the desired temperature by suitable heating means such as an electric heater (not shown). An inert atmosphere of dry nitrogen is introduced under pressure from source 6 into the crucible above the molten bath through a supply line 7. Asthe rod passes through the molten bath of metal in the crucible, molten copper accretes progressively thereon thereby forming a rod of increased diameter with molten metal substantially bonded to the core rod. (See FIG. 2.)

An elongated tube 9 extends upwardly from the crucible 8 and the resulting cast rod having copper accreted thereto is passed out of the crucible through the extension tube 9. The cast rod emerging from the crucible and extension tube is at a relatively high temperature and is cooled somewhat by cooling means 10 such as a water spray nozzle before the rod is passed through a regulated drive motor 11 desirably having incorporated therein a suitable shock isolation loop. From there, the cast rod is directed to a suitable drawing apparatus and storage area as desired.

The extension tube 9 is provided with an inside diameter larger than the diameter of the cast rod. Water emitted from spray nozzle 10, if permitted, would enter tube 9 and crucible 8 where it is vaporized and/or decomposed, which would contaminate the molten bath and cast red, as explained above. In accordance with the present invention, dry nitrogen is continuously supplied to the crucible under sufficient pressure to maintain a continuous flow of nitrogen .gas outwardly from the crucible through the extension tube, thereby purging the system, as explained hereinafter in greater detail.

It will be observed that the dip forming operation is conducted at relatively high temperatures. For example, in a dip forming operation for forming copper rod, the molten bath is maintained at a temperature of about 1120 C. and consequently, the surrounding environment is hot. The surface temperature of the cast body as it emerges from the molten bath is in the order of 1000 C. The temperature of the cast rod will remain essentially constant within the extension tube, cooling only slightly as it passes upwardly from the bath. The outside of the tube is not intentionally cooled by some external means other than the atmosphere, and therefore the environment between the cast rod and tube will remain substantially above the boiling point of water. As a consequence, water emitted from the spray nozzle and entering into the extension tube will be atomized and/or vaporized by the high temperatures.

The extension tube should be of suflicient length statistically to vaporize any water entering the tube. That is, water entering the annulus between tube wall and cast rod is probably first atomized, or partially atomized and partially vaporized, and the tube should be long enough to provide sufficient dwell time for the water to be substantially vaporized. In order to prevent water from penetrating to the crucible, nitrogen is supplied to the crucible under suflicient pressure so that everywhere in the annulus the flow is outward. This is established for laminar flow where the area mean gas velocity (outflow velocity) exceeds one-third the rod velocity, as derived from the well known Navier-Stokes equation, as follows:

I is the static pressure, a is the viscosity coeflicient, and v is the velocity in x direction. The area means velocity is defined as the ratio of the total volume flow to annular space between the rod and wall tube. Also, this velocity changes with temperature in that as the temperature decreases, the density of the gas increases and consequently the velocity decreases. Therefore, reference to area mean velocity is with respect to the minimum volume flow within the extension tube. A solution to the Navier-Stokes equation was plotted graphically in FIG. 3 to show the velocity profile. In the graph, the ratio of gas velocity to rod velocity is plotted as the abscissa and the ratio of the distance from the rod to the difference in radii of the rod and tube as the ordinate. The graph is for the case of the area means velocity equaling one third the rod velocity, and illustrates the minimum condition for no inflow. The resulting vapors are purged from the system by the continuous outflow of nitrogen, but it should be understood that the purge stream might include some finely dispersed liquid droplets as well. Also, this analysis is based on laminar conditions, and because turbulent conditions might also be present, it is essential to exceed more than one-third the rod velocity. It should be understood that the operating conditions for purging the system will vary depending upon such factors as the materials to be dip formed or cast, the core rod size and cast rod size, the rod speed, the operating temperatures, etc.

To further illustrate the invention, copper rod was formed by passing a copper core rod having a diameter of 0.38 inch through a molten bath of copper. The cast rod emerging from the bath had a diameter of 0.625 inch and was moving at a rate of 200 feet per minute through an elongated extension tube measuring three feet in length and having an inside diameter of one inch. Nitrogen gas was fed to the crucible at a rate of two cubic feet per minute or at a pressure of one-half pound per square inch gauge, thereby maintaining a continuous outflow of the purge stream from the system. The resulting cast rod exhibited a high quality being substantially free from irregularities and contamination.

What I claim as new and desired to secure by Letters Patent of the United States is:

1. In a method of casting comprising accreting material onto a core rod by passing said core rod through a bath of molten casting material contained in an enclosed crucible for thereby accreting said molten material on said core rod and passing the resultant cast rod comprising said core with accretedmolten material emerging from said crucible outwardly therefrom for being solidified and cooled, the improvement of cooling the said emerging cast rod with a liquid coolant while avoiding contamination thereby of the atmosphere in said crucible and of the casting material comprising applying liquid coolant to said cast rod in a cooling region spaced from said crucible; passing said emerging cast rod through an elongated tube sealed to said crucible and extending toward said cooling region and of such dimensions and temperature whereby said coolant upon entering said tube is provided sufiicient dwell time to substantially completely vaporize therein; passing said cast rod through said tube at a predetermined velocity; and continuously supplying inert gas to said crucible at a predetermined pressure effective to maintain a continuous flow thereof through said tube between said cast rod and said tube and at an area means gas velocity in excess of at least about one-third of the cast rod velocity, whereby said cast rod velocity and gas flowing through said tube are cooperatively effective for purging vaporized coolant from said elongated tube and from the space above the surface of said molten material in said crucible.

2. In a method of casting comprising accreting copper onto a core rod of copper by passing said core rod vertically through a bath of molten copper contained in an enclosed crucible for thereby accreting molten copper on said core rod and passing the resultant cast rod comprising said core with accreted molten copper emerging from said crucible outwardly therefrom for being solidified and cooled, the improvement of cooling the said emerging cast rod with water while avoiding contamination by the water or water vapor of the atmosphere in said crucible and of the molten copper comprising spraying coolant water on said cast rod as it passes through a spray region spaced above said crucible; passing said emerging cast rod through an elongated environmentally heated thus sealed at its lower end to the exit of said crucible and which extends vertically toward said spray region and is of such length, diameter and temperature whereby said water upon entering said tube is provided suflicient dwell time to substantially completely vaporize in an elongated, substantially annular space between said cast rod and tube; passing said cast rod through said tube toward said spray region at a predetermined velocity; and continuously supplying inert gas to said crucible at a predetermined pressure effective to maintain a continuous flow thereof out said tube through said cylindrical space between said cast rod and said tube and at an area mean gas velocity in excess of at least about one-third of the velocity of the cast rod passing through said tube, whereby said cast rod velocity and gas flowing through said tube are cooperatively effective for purging vaporized coolant water from said elongated tube and from the space above the surface of said molten copper in said crucible.

3. The method of claim 2 wherein the inert gas comprises nitrogen gas.

6 References Cited 5 DANIEL J. FRITSCH, Primary Examiner US. Cl. X.'R.

UNITED STATES PATENT OFFICE 5 9 CERTIFICATE or CQRREQTION Patent No. 3,813L26O Dated May 2 19 4 Inventor(s) Norman J. Lipstein It is certified that error appears in the aboveidentified-pa'tent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 28 "accretedmol'ten" should be accreted molten Column 4, line 48, "vaporized" shouldbe vaporize Column 4, line 65, "thus" should be tube Signed and sealed this 8th day of October 1974.

(SEAL) Attest:

MCCOY M, GIBSON JR. c. MARSHALL DANN Attesting" Officer Commissioner of Patents 1 I 

